Amine treating and dehydration of gases



May 12, 1953 H. D. FRAzlER 2,638,405

AMINE TREATING AND DEHYDRATION 0F GASES Filed Oct. 51, 1947 IN VEN TOR.

ATTORNEY Patented May 12, 1953 t AMINE TREATING AND DHYDRATION OF GASES Y Henry D. Frazier, Alhambra, Calif., assigner to The Fluor Corporation, Ltd., Los Angeles, Calif., a corporation of California Application October `31, 1947, Serial No. 783,323

Claims. (Cl. 234-2) This invention. has to do with the treatment of gaseous mixtures for the removal of acidic constituents and moisture, and is applicable generally to the treatment of hydrocarbon gases such as natural and refinery gases for their dehydration and removal of acidic impurities such as hydrogen sulfide and carbon dioxide. Particularly the invention is directed to an improved process whereby the same amine composition absorbent may be employed for both dehydration and acid gas absorption. f

Heretofore aqueous amine solutions have extensively been used in gas treating for the removal of acidic impurities. Where required, dehydration of the gas has necessitated use of an additional absorbent, such for example as a solid or liquid desiccant through which the gas is passed following extraction of acidic impurities, or a hygroscopic glycol in the amine solution. Thus vthe amine solutions themselves have not been moisture absorptive, at least to any extent capable of dehydrating the gas to the degree required to prevent moisture precipitation and resultant hydrate vformation in the ground pipes. One of my major objects is to utilize an aqueous solution in a manner permitting eiTicient, and if desired selective, absorption ofan acidic impurity, and to employ the same amine for dehydration of the gas, all by a simple cyclic contacting and regenerating process.

In general Vthe invention contemplates vcontacting the gas in a rst zone with `an aqueous solutionof the amine having such fluidity as to assure intimate and eicient gas-liquidcontact, as well as high transfer rates in the heat exchange equipment, and then contacting the gas in ka lsecond zone with a solution of the same amine suiciently concentrated to dehydrate the gas. )As will appear, the invention is adaptable to single column stage treatment in which the dehydrating amine enters the first contacting zone to supplement and serve as the acid gas absorbent. A vfurther distinctive aspect of the invention is'the method of regenerating the total amine absorbent, whereby a major portion is heated to liberate its absorbed acidic impurities and returned tothe contactor in aqueous solution having the abovementioned characteristics, while a second portion of the amine is regenerated and dehydrated to the degree required for drying they gas in the second contactor stage.

The invention has various additional objects such as the use of an aqueous amine solution capablek of selectively absorbing hydrogensuliide as against carbon dioxide, and the particular materials, steps and operations involved in the gas treatment. All these will be explained to best advantage in the following detailed description in which reference is had to the accompanying drawing illustrative of a typical process in flow sheet form.

The amines, or mixture of amines employed, are'characterized by various properties rendering them particularly adaptable for the several purposes of gas purification and dehydration,

while maintaining high contact and heat transfer efficiency. Preferably I use'a water soluble amine having a boiling temperature in excess of 200 C. and low viscosity in the water solutions employed. For dehydration purposes, the selected amine will inA concentrated' solution be hygroscopic to a degree such that it will absorb and reduce the moisture content of the gas to an extent such that no moisture will condense out of the gas at the usual ground temperatures to which the usual gas distribution pipes are subjected. As illustrative, I may use such high boiling temperature, normally liquid amines as methyldiethanolamine or triethylenetetramine, having the properties referred to above'. Some of these amines may be used to further advantage Where the prime consideration in purifying the gas is removal of its hydrogen sulfide content, in that such amines in aqueous solution are found to be preferentially absorptive of hydrogen sulfide as against carbon dioxide. Thus whereas all the hydrogen sulfide may be absorbed to produce a lead acetate sweet gas, the carbon dioxide is not correspondingly or equivalently absorbed and the bulk of the carbon dioxide content will remain unaffected.

Referring to the drawing, the gas containing moisture together with hydrogen sulfide and carbon dioxide as impurities, is fed through line l0 into the bottom of a contactor column il which may contain bubble trays I2 or other suitable means for effecting intimacy of contact between the liquid and gas. The treated and dehydrated gas leaves the contactor through line t3. Rising within a lower section Ila of the column, the gasis contacted with a down flowing stream of aqueous amine solution introduced to the contactor through line I4.v Typically the absorbent will comprise an aqueous solution containing 20-40% amine by weight, and 30 to 80% water. Leaving the lower column section Ila, the gas flows through an upper section IIb in contact with a concentrated solution of the amine, i. e. a hygroscopic solution of the amine containing under about Water. While serving primarily to dehydrate the gas, the concentrated solution serves the additional function in the top section IIb of absorbing any uncombined hydrogen sulfide passing from the section ila. Upon entering the lower section, the dehydrating solution supplements th ainiie absorbent introduced through line I4, to react With the hydrogen sulfide content of the gas.

Leaving the bottom of the contactor-through line I5, the rich absorbent flows thrciigh Achiedi* more heat exchangers I6 and line I'I to the still I8 which may be of the usual type employed for amine solution regeneration in gas `treating plants. After flowing downwardly through the l still countercui'rently to released gasesand water vapor, the absorbent enters the 'eboile It through line and is heated to a temperature suflicient to drive off at least all but a small percentage of the absorbedimpurities, and to concentrate the' solution ji'yitliin the range previ ly ascribed totheabscrbiit introduced tothe contactor th'rcugh line i4. The 'gases and vapor re'- eased in the 'i-eboiler are retu'rn'ed to the "still colii'nn through line 2l. A fr 'a'jcr pfortih, say 80% to 90%, ofthe amine solution le'avi 'gftli' reboiler throughl line 22 is recirculate'd by piiinp ;I 'thi'igh line 2d and'e'xchahger `Iii forturn to th" contacter Way of line 2h vand c'olerl.

'iii r'iiiaiiiirg `iortion of tire solution is 'ii'v rteri f line 22 through iine 221 to ajc'onfc'eiitra ofi* 28 ein theshitio'n is ydeliydrated stiflicieiitly to s'rfve as the moisture absorbent in the top "section Hb ,of the contacter. `Water vap ahdaiiy residual 'liberated acid gas passfrin hrougii iiiie ze iiitttiierebiir to the still, `'r independentlyofthe rebjoiierit di sate is returned' by; purip si through' iiiie sa "to tjs-stings r'fiiix. It' lv viii be untiersttpri that the system operated `under pre`s`s`ur's co moniy atipici/d in treatment and regen'- for 'tiiere'moval' ofiiioisture and an 'acidic confs'tituent? that includes contacting the gasiri'a first'zfoiie With "a solution consistinge se of a hygros'cop icain` 'ii;ie and Water to reino acidic 'constituent 'by its reaction with theam then contacting the gas in a second tone 'l solution of vsaid ainine `sui'ii'ciently "concen t'ed to substantially dchydrate the gas by virtue' "of hygros'copicity o ftli'eamine, passing all'the'ar'n'ine through 'heating and regenerating yzone" ltoA regejnerate thefaniinesolution and returning a por; tot rf it@ regenerated solution-tos'aid tra tdt-e, and passinganother fportion of the regenerated solutionj through a' heating and' concentrati g sone Whfe'iein the solution is concentrated by L hydration andi ui'ni'ng the dehydratedsclution tosaid secondfzo'ne y .t 7o tuent, thatl includes contacting the gas -fin a lfl'rst solution of said amine sufficiently concentrated to substantially dehydiate the gas by virtue of hygroscopicity of the amine, passing all the amine through a heating and regenerating zone to regenerate the amine solution and returning a relatively large portion of the regenerated solution to said lfrstz'ones and passing another-,and relatively small portion of the regenerated solution through a heating and concentrating zone wherein the solution is concentrated by dehydration and returning the dehydrated solution to said second Zone.

3. The method of treating a gaseous mixture vfor the rernoval of moisture and an acidic constituent, ,that includes contacting the gas in a first zone With an aqueous solution of an amine to rniove sai'd acidic constituent by its reaction with the amine, said amine having a boiling temperature in excess of 203 C., then contacting the gasvin a second zone with a solution of said amine 's iiicieiitly conc'eiitrat'edv to 'substantially vdehydr'ate the passing all the ainih'e through a heating andre'generating Zonev to regenerate the aihine's'olution and returning 'a 'portion of the' regenerated solution to said rst Zone, and'passing 'another portion of the regenerated 'solution through a heating and concentrating fzcne'vvherein the solution is concentrated by dehydration and returning the dehydrated solution to said second'zon'e.

4. The method of treating' a ga's'eousiniirtiirc for the removal of in'oistur'e andan acidic "constituenty that includes contacting the gas in "a rst Zone With an aqueoussol'ution 'of an aniihe torer'n'ove 'said acidic constituent byitsre'ac'tion With the amine, said solution containing iciri 3G to 30 percent Water, then contactingV the gas in a 'second zone with a solution of said 'anir'ie suiiiciently concentrated to substantially dehydrate the gas, the last mentioned solution cntaini'ng less than 10 perC'entWate'r, passing all the inin'e through 'a heating and regenerating cone to regeneratethe ai'nine solution ahdr'eturr'iing a portion 'of the regenerated solution to said first ione, and passinga'nother portion' of the regenver'ated solutionthr'ough a heatingand concentratingzone 'wherein the solution is concentrated by dehydration vand returning the dehydrated solution to `said second Zone.

5. The inetlio'dof treating a gaseous mixture forthje removal 'of moisture and an acidic cohs'titunt, that includes "contacting the "gas in a 'zdif'iewit'h vva solution consisting essentially of ahygroscopic'ainine ahdwater 'to r'eiri've 'said acidiccoiistitueht by 'its reaction with the amine, thcn'cnta'ctih'g the gas in fa second la'o'n'e a solutionofs'aid aihi'ne su'i'ciently'e'oh entrated to`r substantially dehydrate the gafsby v'i'rt'ii'e'bf iiygroscopiityor trieY amine, passing' the' amine solution frein said ione' into the sc'co'iidone, passing lall the ariiii'e vfrom the second Ziie througha heating 'and re'gei'ierating'one to 'cgenerate the amine solution and returning a portionof the regenerated solution to said hrstzone, and; vpassing 'anotherpi't'ion of theregene'rated solution tliinugh a heating and concentrating zone Wjl'ierciny the "solution in 'concentrated' by dehydration and returning the vdeiiytiiateoistint'ion to said "second zone.

`6. The niethod 'of' treating a`gaseo"u`s' 'miit'iire for' the rcnoval Yof' moisture and an acidic constituent, th^" ncliides contactingth'e :gas in "a fi time i fi'titii a soiiition Ctiijsistiirg fssent'iaiiy or iiy'grqs'copic airline-'arid waterjt'o remove 'said loi c-"c'risti'tent vtyi'tsr reaction with the amine.

then contacting the gas in a second zone with a solution of said amine suiciently concentrated to substantially dehydrate the gas by virtue of hygroscopicity of the amine, passing all the amine through a heating and regenerating zone to regenerate the amine solution and returning a portion of the regenerated solution to said iirst zone, passing another portion of the regenerated solution through a heating and concentrating zone wherein the solutionis concentrated by dehydration and returning the dehydrated solution to said second zone, and passing vapors released from said concentrating zone into said regenerating zone.

7. The method of treating a gaseous mixture for the removal of moisture and an acidic constituent, that includes passing the gas upwardly through successive lower and upper Zones in a contactor column, contacting the gas in said lower zone with a down-flowing solution consisting essentially of a hygroscopic amine and water to remove said acidic constituent by reaction with the amine, then contacting the gas in said upper Zone with a solution of said amine suiiiciently concentrated to substantially dehydrate the gas, passing all the amine through a heating and regenerating zone to regenerate the amine solution and returning a portion of the regenerated solution to said lower Zone, and passing another portion of the regenerated solution through a heating and concentrating zone wherein the solution is concentrated by dehydration and returning the dehydrated solution to said upper zone.

8. The method of treating a gaseous mixture for the removal of moisture and an acidic constituent, that includes passing the gas upwardly through successive lower and upper zones in a contacter column, contacting the gas in said lower zone with a down-iowing aqueous solution of an amine to remove said acidic constituent by reaction with the amine, said amine being hygroscopic and having a boiling temperature in excess of 200 C. then contacting the gas in said upper zone with a solution of said amine sufficiently concentrated to substantially dehydrate the gas, passing all the amine through a heating and regenerating zone to regenerate the amine solution and returning a portion of the regenerated solution to said lower zone, passing another portion of the regenerated solution through a heating and concentrating Zone wherein the solution is concentrated by dehydration and returning the dehydrated solution to said upper zone, and passing 6 the amine solution from said upper zone downwardly through the lower zone.

9. The method of treating a gaseous mixture for the removal of moisture and an acidic constituent, that includes contacting the gas in a first zone with an aqueous solution of an amine to remove said acidic constituent by its reaction with the amine, said amine being hygroscopic and having a boiling temperature in excess of 200 C. then contacting the gas in a second zone with a solution of said amine sufliciently concentrated to substantially dehydrate the gas, removing the amine from said zones and heating and regenerating a first portion thereof and returning said portion to the rst zone in aqueous solution, and heating and regenerating a second portion of the removed amine under temperature and pressure conditions such that said second portion contains substantially less moisture than said first portion, and returning said second portion to said second Zone.

10. The method of treating a gaseous mixture for the removal of moisture and an acidic constituent, that includes contacting the gas in a rst zone with a solution containing water and methyldiethanolaniine to remove said acidic constituent by reaction with the amine, then contacting the gas in a second zone with a solution of said amine sutciently concentrated to substantially dehydrate the gas, passing all the amine through a heating and regenerating zone to regenerate the amine solution and returning a portion of the regenerated solution to said rst zone, and passing another portion of the regenerated solution through a heating and concentrating zone and returning the concentrated solution to said second zone.

HENRY D. FRAZIER.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date Re. 18,958 Bottoms Sept. 26, 1933 2,083,213 Baehr et al. June 8, 1937 2,106,446 Baehr et al Jan. 25, 1938 2,161,663 Baehr et al June 6, 1939 2,177,068 Hutchinson Oct. 24, 1939 2,311,342 Kerns et al Feb. 16, 1943 OTHER REFERENCES Bottoms, R. R., Organic Bases for Gas Purication, I. and E. Chemistry, vol. 23, No. 5, May 1931, pp. 501-504. 

10. THE METHOD OF TEATING A GASEOUS MIXTURE FOR THE REMOVAL OF MOSITURE AND AN ACIDIC CONSTITUENT, THAT INCLUDES CONTACTING THE GAS IN A FIRST ZONE WITH A SOLUTION CONTAINING WATER AND METHYLDIETHANOLAMINE TO REMOVE SAID ACIDIC CONSTITUENT BY REACTION WITH THE AMINE, THEN CONTACTING THE GAS IN A SECOND ZONE WITH A SOLUTION OF SAID AMINE SUFFICIENTLY CONCENTRATED TO SUBSTANTIALLY DEHYDRATE THE GAS, PASSING ALL THE AMINE THROUGH A HEATING AND REGENERATING ZONE TO REGENERATE THE AMINE SOLUTION AND RETURNING A PORTION OF THE REGENERATED SOLUTION TO SAID FIRST ZONE, AND PASSING ANOTHER PORTION OF THE REGENERATED SOLUTION THROUGH A HEATING AND CONCENTRATING ZONE AND RETURNING THE CONCENTRATED SOLUTION TO SAID SECOND ZONE. 